BOSTON (AP) - Celtics coach Brad Stevens has said what has carried his team through the NBA postseason is its ability to make "winning plays" with the game on the line.

And more times than not, it's been Marcus Smart making them.

Since returning from thumb surgery late in the first round, Smart has been unflappable and Boston's unquestioned deacon of toughness.

From sacrificing his body diving for loose balls or keeping plays alive with a rebound , to causing deflections on defense, to popping up out of the crowd for a timely rebound or tip-in, Smart is the proud everyman for a once underdog Celtics team that has outworked the Cavaliers through the first two games of the Eastern Conference finals.

"That's me. That's how I was raised," said Smart, who was Boston's top performer off the bench in the Celtics' 107-94 Game 2 win with 11 points, nine assists, five rebounds and four steals. "I'm the youngest of four boys. My whole life I had to fight.

"I had to get down and do things in order to secure my spot in the household. So coming onto the court it's nothing different."

Boston took a 2-0 series lead on the Bucks in the first round before dropping back-to-back games in Milwaukee. Smart came off the bench when the series swung back to Boston for Game 5. He finished that one with nine points, five rebounds, four assists and three blocks to help the Celtics pull out a five-point victory.

Boston is 8-2 since Smart's return and has the Cavaliers facing their first 2-0 series hole since 2008, when they lost 4-3 to the Celtics in the conference semifinals. Boston went on to win the NBA title that season.

Not bad for a guy taken sixth overall by Boston in the 2014 draft despite being criticized coming out of Oklahoma State for being undersized at 6-foot-4, having questionable ball-handling and poor 3-point shooting, and at times displaying uncontrollable emotions.

"I think he's as tough as they come," Stevens said. "He matches his intensity with a physical toughness. ... People talk about him all the time. Sometimes they focus on things that don't matter, and the other times they focus on that he impacts winning."

Smart showed all those attributes late in the fourth quarter Tuesday night against the Cavs, when he came to the defense of Al Horford after JR Smith shoved him in the back on a layup attempt. Smart got in Smith's face, prompting Smith to shove him. Both received technical fouls. But having a teammate's back is second nature to Smart.

He said he felt like Smith was being a bully . That has never played well in Smart's orbit.

"One of my guys was down, and I took offense to it," he said.

From a basketball standpoint, Cleveland has taken note of Smart's impact.

LeBron James called Smart's creativity on the court "uncanny," and Kevin Love said the Cavs can "definitely learn" from what Smart and Boston are doing to them.

"I think Marcus always makes plays at the right time," James said. "They put the ball in his hands and they trust him to make plays for others."

Cavs coach Tyronn Lue said Smart's impact is clearly something they must combat as they try to hold serve at home beginning with Game 3 on Saturday.

"If it's 50/50 balls, he's going to get it. If it's a loose ball, offensive rebound they need to have, he's going to get it," Lue said. "We've got to be able to find someone who can match his toughness."

The most impressive thing about Smart's run might be that he's doing it while his mother, 63-year old Camellia Smart, is battling bone marrow cancer.

Smart learned of her diagnosis during a visit to see her in Texas back in April.

"We're just trying to preserve life," Smart said recently of how she's doing. "At her age a transplant would probably be more harmful than good. ... It's tough, but my mom's a tough cookie.

"As long as she's fighting I'm going to continue fighting."

It's the kind of toughness that has always run deep in the Smart family. His mother also has been through quadruple-bypass surgery on her heart.

She wants her son exactly where he is.

"She told me she'd rather me be here than back there, doing what I love to do," Smart said, "because she loves watching me play. She said it puts a smile on her face."